1. Field of the Invention
The present invention relates to a solid-state image sensor, a method of manufacturing the same, and a camera.
2. Description of the Related Art
On-chip color filters and microlenses are formed as optical components to improve the sensitivity of solid-state image sensors such as CMOS sensors which have been conventionally used for digital cameras and digital video cameras. A typical method of manufacturing a solid-state image sensor will be described with reference to FIGS. 3A and 3B. FIG. 3A is a sectional view of the peripheral circuit region of a solid-state image sensor. FIG. 3B is a sectional view of a pixel region of the solid-state image sensor. In a manufacturing process for a solid-state image sensor, after circuit elements such as photodiodes and transistors are formed on a semiconductor substrate, signal lines (conductive patterns) 122 for signal transfer can be formed.
Forming an insulating film covering the signal lines 122 can form an interlayer dielectric film 121 enclosing the signal lines 122 and can also form wiring lines 123 as power supply lines or signal lines on the interlayer dielectric film 121. Since there are gaps between a plurality of conductive patterns constituting the wiring lines 123, unevenness is formed on the surface of the substrate including the wiring lines 123. Coating the surface of the substrate with a resin by using a spin coat method can form a planarizing layer 131. In addition, it is possible to form a color filter 132 by coating the planarizing layer 131 with a pigment dispersant resist or a dye dissolved resist by the spin coat method and performing exposure and development processes on the resultant structure. A planarizing layer 133 can be formed on the color filter 132 by the spin coat method. Thereafter, it is possible to form microlenses 134 by coating the resultant structure with a photosensitive resin serving as a microlens material by the spin coat method and performing exposure, development, and baking processes on the resultant structure.
There is a tendency toward an on-chip structure having a digital circuit arranged in a peripheral circuit region for improvements in the quality and speed of a solid-state image sensor. A current flowing in such a digital circuit greatly varies. If the width of each wiring line 123 as a power supply line or a signal line arranged in the layer above a signal line exhibiting a large current variation is increased, the potential can become unstable due to the strong influence of variations in current flowing in the signal line 122 below the wiring line 123. It is therefore difficult to increase the width of the wiring line 123.
If, however, the width of each wiring line 123 decreases, since the area of each concave portion on the surface of the substrate increases, large unevenness 150 can be formed on the surface of the planarizing layer 131 formed on the wiring lines 123. The unevenness 150 on the surface of the planarizing layer 131 can be formed not only in the peripheral circuit region but also in the pixel region. The unevenness 150 on the surface of the planarizing layer 131 tends to increase at the time of formation of the planarizing layer 131 by the spin coat method. As a consequence, large unevenness can be formed not only in the peripheral circuit region but also in the pixel region. This is because, when the planarizing layer 131 is formed by the spin coat method, unevenness on the surface of the underlayer will cause coating unevenness in a region wider than the region in which the unevenness exists, and the coating unevenness forms the film thickness distribution of the planarizing layer 131.
If unevenness exists on the surface of the planarizing layer 131 under the color filter 132, the film thickness of the color filter 132 can become uneven, or the shape of the microlenses 134 formed on the color filter 132 can become uneven. This can lead to a deterioration in the quality of images captured by the solid-state image sensor.
Japanese Patent Laid-Open No. 5-21771 has proposed a method of planarizing a surface by filling the distribution of concave portions with a polymeric material. This method, however, increases the number of steps.